In automotive engineering, it is already known to incorporate a permanent-magnet-excited synchronous machine (PM synchronous machine) into the drive train of a vehicle, between the internal combustion engine and the transmission, as an integrated crankshaft starter/generator.
A PM synchronous machine of this kind is controlled in a rotor-field-oriented coordinate system. An example of a field-oriented current control system for a PM synchronous machine having a pulse-width-modulated inverter is shown in FIG. 1. It is based on an actual-value measurement of the phase currents of a three-phase current system and on a determination, based on the measured actual values, of a longitudinal and a transverse component of the control voltage with respect to the rotor position. The transverse current is proportional to the desired torque.
In this control system, the phase currents ia, ib, ic derived from the three-phase system of the PM machine are converted, in a Park transformer 13, into currents Id_actual and Iq_actual of a rectangular coordinate system. Current Id_actual represents the actual value for the machine's longitudinal current. Current Iq_actual designates the actual value for the machine's transverse current.
Actual longitudinal current value Id_actual is conveyed via a superimposition element 12 to a longitudinal current controller 1, and actual transverse current value Iq_actual as the actual value to a transverse current controller 2. Superimposition element 12 receives, as a further input signal, a feedback signal that is obtained from output variable uq′ of a steady-state decoupling network 5. In addition to providing the decoupling that is important for the control system, steady-state decoupling network 5 also performs the task of achieving, in coaction with output limiters 3 and 4 and an anti-windup procedure at longitudinal current controller 1, a field attenuation in the upper rotation speed range. This field attenuation of the PM synchronous machine at higher rotation speeds is necessary because otherwise the induced machine voltage would be greater than the maximum power converter output voltage. The latter voltage is limited by the supply voltage, which is the motor vehicle's electrical system voltage. In this field attenuation mode, the power converter is operated in an overmodulated state so that the power converter output voltage is no longer sinusoidal.
A setpoint signal generated by a longitudinal current setpoint generator 9 is conveyed to the setpoint input of longitudinal current controller 1, and a setpoint signal generated by a transverse current setpoint generator 14 is conveyed to the setpoint input of transverse current controller 2. Transverse current setpoint generator 14 generates the transverse current setpoint signal as a function of the output signal of a battery voltage sensor.
A control variable Id* for the longitudinal current is made available at the output of longitudinal current controller 1, and a control variable Iq* for the transverse current at the output of transverse current controller 2. These control variables are conveyed to steady-state decoupling network 5 which, using the aforesaid control variables, ascertains a longitudinal voltage component ud′ and a transverse voltage component uq′ for the control voltage of the PM synchronous machine.
These control voltage components ud′ and uq′, which are control voltage components in the rectangular coordinate system, are conveyed via respective output limiters 3 and 4 to an inverse Park transformer 6. The purpose of the latter is to convert the limited control voltage components ud and uq, present in the rectangular coordinate system, into control voltage components ua, ub, and uc of the three-phase system. These are converted, in a pulse-width-modulated inverter 7, into triggering pulses for PM synchronous machine 8.
Transverse voltage component uq′ of the control voltage, which is outputted at the output of steady-state decoupling network 5, is conveyed to absolute value generator 10, which ascertains the absolute value |uq′| of the aforesaid transverse voltage component.
The output signal of absolute value generator 10 is used as the input signal for a threshold value switch 11. If the absolute value |uq′| exceeds a predefined threshold value, a value of 0 is then outputted at the output of threshold value switch 11. If the absolute value |uq′| falls below the predefined threshold value, a value of 1 is then outputted at the output of threshold value switch 11.
Exemplified embodiments for the configuration of a decoupling network in which a steady-state machine model is stored are described in the Applicant's DE 100 44 181.5.
DE 100 23 908 A1 discloses a method for ascertaining the magnet wheel position of an electrical machine (which is, for example, a three-phase generator with pulse-width-modulated inverter), a rotor winding, a stator equipped with inductances, and a voltage source disposed between two phase terminals additionally being provided. With this method, circuit elements can be used to branch into two phases, in which the respective phase voltage profiles are measured. Superimposing them allows an unequivocal determination of the magnet wheel position. With the known method, the rotor positions for each of the voltage profiles are stored in table form.
The periodical ETEP, Vol. 8, No. 3, May/June 1998, pp. 157–166, furthermore describes a permanent-magnet-excited synchronous machine with a field attenuation mode, in which a large ratio exactuals between the maximum and basic speeds. This is achieved by way of an additional negative D component of the stator current. In the context of regulation of the known synchronous machine, a measurement of the rotor position is performed using the output signals of three Hall sensors, one Hall sensor being associated with each of the phases U, V, W.
DE 199 28 481 A1 discloses a method for generating control variables for the longitudinal and transverse voltage to represent respectively the flux-forming current and torque-forming current in a field-oriented control system for rotating-field machines in consideration of the stator voltage drop and the steady-state internal voltage, in which the steady-state internal voltage is calculated on the basis of setpoint variables of the currents. Also known from this document are a method for ascertaining the angular rotor frequency of an asynchronous machine controlled in field-oriented fashion, and a method for sensing and pairing at least two phase currents of an asynchronous machine in order to implement a field-oriented control system.